1. Field of the Invention
The invention generally relates to wireless LAN (Local Area Network, WLAN) systems and in particular to gain controlled wireless LAN devices such as receivers, access points or stations, and corresponding methods that provide or use a digital signal having a normalized signal level.
2. Description of the Related Art
A wireless LAN system is a flexible data communication system that allows a remote user's mobile device to connect to an access point of the network (wired LAN), without having the requirement for the mobile device of being physically attached to the network, as well as to connect to a further remote user device. Thus the mobile device in a wireless LAN system provides for wireless mobility and additionally achieves the common functionality of wired data transfer as well as application and data access via the network.
As illustrated in FIG. 1, a wireless LAN 1 provides connection for mobile devices 4, 5, which are also referred to as (mobile) stations hereafter. As indicated by arrows, the mobile devices 4, 5 may communicate with an access point 3, which is connected to a wired network 2. Further the mobile devices 4, 5 can interconnect each other as well. Hence, data transfer between one of the mobile stations 4, 5 and one of wired devices 6, 7 via the access point 3 or another one of the mobile stations 4, 5 can be established.
Presently, Radio Frequency (RF) and Infra Red (IR) transmission techniques are most commonly used in wireless LANs. The industry specification IEEE 802.11 provides a standard for wireless LAN systems and products and describes direct sequence spread spectrum (DSSS) as one possible modulation technique for RF signals. Particularly upon using DSSS modulation, but also when using other modulation techniques, a wireless LAN device internally requires a stable signal level for correctly evaluating a received signal. Hence, a change in the quality of the received signal has to be compensated before further evaluating the signal. For this purpose automatic gain control (AGC) circuits are provided.
Frequently, AGC circuits are analog circuits that receive an analog signal and generate a gain control signal for a variable gain amplifier to amplify the signal. However, an analog AGC circuit typically requires a complex structure of subunits for generating the gain control signal. Particularly in view of the desire to reduce the size of mobile devices this is a major disadvantage of analog AGC circuits. Additionally, analog AGC circuits suffer from their relatively long reaction time to fast or significant changes in the input signal.
Further AGC circuits exist that comprise digital units to calculate the AGC control signal. These circuits however, due to the quantization of their internal values and the corresponding quantization of the AGC control signal, typically add some kind of oscillation to the output signal of the variable amplifier. The oscillation may hinder the correct evaluation of the amplified signal.
Hence, conventional AGC circuits for wireless devices are expensive high quality parts, since they need to be built in a complex structure for providing a precise output signal level. Reducing the requirements on the AGC circuits would however decrease system performance and reliability of the wireless LAN system.